Phenol resin

ABSTRACT

The present invention relates to a phenol resin, in particular a phenol resin for resists suitable for forming resist patterns. The phenol resin of the present invention is obtained by reacting at least two components, i.e., a compound (A) such as 4-hydroxymethyl-2,6-dimethylphenol and a polymerizable phenol compound such as parahydroxystyrene or a polymer (B), which is a polymer of the polymerizable phenol compound, in a ratio of 1 to 50 moles of the compound (A) to 100 moles of the polymerizable phenol compound or 100 moles of structural unit of the polymerizable phenol compound contained in the polymer (B) in the presence of an acid and having a molecular weight of 2,000 to 20,000. Such a phenol resin provides good pattern shape, heat resistance, resolution, and sensitivity in resists for lithography.

This application is based on Japanese Patent Application No. Hei11-158797 and No. 2000-109779, the contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a phenol resin, in particular to aphenol resin for resists suitable for use in forming resist patterns.

2. Background Art

With the recent high degree of integration of integrated circuits,pattern formation at quarter micron levels has been desired. As a meansfor achieving downsizing of patterns, mention may be made of a methodfor shortening the wavelength of the light used. As such, in particular,use of a KrF excimer laser has enabled production of 64M DRAMs and 256MDRAMs and hence has been paid much attention.

Under the circumstances, there has been an increasing demand for resistmaterials for high resolution lithography and a resist material thatshows good pattern formation ability and has improved heat resistance,resolution and sensitivity has been keenly desired.

In accordance with the downsizing of patterns, there has been a shift inthe etching process of wafers from wet etching to dry etching. As aresult resists are required such that the heat upon dry etching does notdeform their patterns, and hence improvement in the heat resistance ofresists has been demanded.

Resists must be transparent to the above light source, so mainlypolyvinylphenols have been used. However, they are insufficient inpattern shape, resolution, developability, and film retention propertiesand modification of polyvinylphenols has heretofore been performed.Modification of polyvinylphenols by hydrogenation and modification byvarious types of copolymerization with styrene monomers, acrylicmonomers, etc. have been carried out to promote functionalization ofpolyvinylphenols. However, in pattern formation at sub-quarter-micronlevels, there has been found no resist material that simultaneouslysatisfies the requirements for good pattern shape, resolution,sensitivity, developability, film retention properties, and heatresistance.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a phenol resin thatgives good pattern shape, heat resistance, resolution, and sensitivitysimultaneously in resists for lithography, etc.

As a result of intensive research with a view to achieving the aboveobject, the present inventors have found that condensation of a compound(A) represented by the following general formula (I) with apolymerizable phenol compound represented by the following generalformula (II) or polyvinylphenol (B) that is a polymer of thepolymerizable phenol compound can give rise to a phenol resin forresists that combines good pattern shape, resolution, sensitivity,developability, film retention properties, and heat resistance, thusaccomplishing the present invention.

That is, the phenol resin of the present invention is a phenol resinobtained by reacting at least two components, i.e., a compound (A)represented by the following general formula (I) and a polymerizablephenol compound represented by the following general formula (II) or apolymer (B), which is a polymer of the polymerizable phenol compound, ina ratio of 1 to 50 moles of the compound (A) to 100 moles of thepolymerizable phenol compound or 100 moles of structural unit of thepolymerizable phenol compound contained in the polymer (B) in thepresence of an acid and having a weight average molecular weight of2,000 to 20,000

(wherein R¹, R², R³, and R⁴, which are the same or different,independently represent a hydrogen atom, an alkyl group, an alkoxygroup, an aryl group, an aralkyl group, a hydroxyl group or a halogenatom)

(wherein R⁵ represents a hydrogen atom or a methyl group, R⁶, R⁷, R⁸,and R⁹, which are the same or different, independently represent ahydrogen atom, an alkyl group, an alkoxy group, an aryl group, anaralkyl group, a hydroxyl group or a halogen atom, provided that atleast one of R⁷ and R⁹ is a hydrogen atom).

Such a phenol resin can provide good pattern shape, heat resistance,resolution, and sensitivity in resists for lithography, etc. and isuseful as a light-sensitive resin such as a resist or as a resinprecursor for obtaining the light-sensitive resin. Use of the phenolresin of the present invention enables improvement in the properties ofresists. The light-sensitive resin composition comprising the phenolresin of the present invention is excellent in the balance of variousproperties of resists.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the general formula representing the compound (A), the alkyl groupsin the substituents R¹ to R⁴ are preferably linear, branched or cyclicand have one or more and 10 or less carbon atoms. As such alkyl groups,mention may be made of, for example, a methyl group, an ethyl group, anisopropyl group, a t-butyl group, a 2-ethylhexyl group, a cyclohexylgroup, etc.

The alkoxy groups in the substituents R¹ to R⁴ preferably have 1 or moreand 4 or less carbon groups. As such alkoxy groups, mention may be madeof, for example, a methoxy group, a propoxy group, a t-butoxy group,etc.

The aryl groups in the substituents R¹ to R⁴ include preferably a phenylgroup, a naphthyl group, a tolyl group, a cumyl group, etc.

The aralkyl groups in the substituents R¹ to R⁴ preferably have 6 ormore and 10 or less carbon atoms. As such aralkyl groups, mention may bemade of, for example, a benzyl group, a phenethyl group, a1-methyl-1-phenylethyl group, etc.

Those preferred as the compound (A) include ones in which R¹ R², R³, andR⁴ are each a hydrogen atom or an alkyl group. As such compounds (A),mention may be made of, for example, 4-hydroxymethylphenol,4-hydroxymethyl-2-methylphenol, 4-hydroxymethyl-3-methylphenol,4-hydroxymethyl-2-ethylphenol, 4-hydroxymethyl-3-ethylphenol,4-hydroxymethyl-2-n-propylphenol, 4-hydroxymethyl-3-n-propylphenol,4-hydroxymethyl-2-isopropylphenol, 4-hydroxymethyl-3-isopropylphenol,4-hydroxymethyl-2-n-butylphenol, 4-hydroxymethyl-3-n-butylphenol,4-hydroxymethyl-2-s-butylphenol, 4-hydroxymethyl-3-s-butylphenol,4-hydroxymethyl-2-t-butylphenol, 4-hydroxymethyl-3-t-butylphenol,4-hydroxymethyl-2,3-diemthylphenol, 4-hydroxymethyl-2,5-diemthylphenol,4-hydroxymethyl-2,6-dimethylphenol, 4-hydroxymethyl-3,5-dimethylphenol,4-hydroxymethyl-2-isopropyl-6-methylphenol,4-hydroxymethyl-2-t-butyl-6-methylphenol,4-hydroxymethyl-2,6-diisopropylphenol,4-hydroxymethyl-2,6-di-t-butylphenol,4-hydroxymethyl-2,3,5-trimethylphenol,4-hydroxymethyl-2,3,6-trimethylphenol, etc.

Particularly preferred compounds (A) are those in which two or three outof R¹ to R⁴ are alkyl groups and the remaining ones are hydrogen atoms.As such compounds (A), mention may be made of, for example,4-hydroxymethyl-2-methylphenol, 4-hydroxymethyl-2,6-dimethylphenol,4-hydroxymethyl-2,3,6-trimethylphenol, etc.

Other preferred compounds (A) include ones in which R¹, R², R³, and R⁴represent independently a hydrogen atom, an alkoxy group, a hydroxylgroup or a halogen atom. As such compounds (A), mention may be made of,for example, 4-hydroxymethyl-2-methoxyphenol,4-hydroxymethyl-3-methoxyphenol, 4-hydroxymethyl-2-hydroxyphenol,4-hydroxymethyl-3-hydroxyphenol, 4-hydroxymethyl-2,6-difluorophenol,etc.

The polymerizable phenol compound to be condensed with the compound (A)and represented by the above general. formula (II) includes avinylphenol compound and an isopropenylphenol compound.

The above vinylphenol compound is a compound that has a vinyl group(CH₂═CH—) at the para-position with respect to the phenolic hydroxylgroup.

AS the vinylphenol compound, the ones in which the substituents R⁶ to R⁹in the above general formula (II) independently represent a hydrogenatom, an alkyl group, an alkoxy group, an aryl group, an aralkyl group,a hydroxyl group or a halogen atom, provided that at least one of R⁷ andR⁹ is a hydrogen atom are preferred.

The alkyl groups in the substituents R⁶ to R⁹ are preferably linear,branched or cyclic and have one or more and 10 or less carbon atoms. Assuch alkyl groups, mention may be made of, for example, a methyl group,an ethyl group, an isopropyl group, a t-butyl group, a 2-ethylhexylgroup, a cyclohexyl group, etc.

The alkoxy groups in the substituents R⁶ to R⁹ preferably have 1 or moreand 4 or less carbon groups. As such alkoxy groups, mention may be madeof, for example, a methoxy group, a propoxy group, a t-butoxy group,etc.

The aryl groups in the substituents R⁶ to R⁹ include preferably a phenylgroup, a naphthyl group, a tolyl group, a cumyl group, etc.

The aralkyl groups in the substituents R¹ to R⁴ preferably have 6 ormore and 10 or less carbon atoms. As such aralkyl groups, mention may bemade of, for example, a benzyl group, a phenethyl group, a1-methyl-1-phenylethyl group, etc.

Those preferred as the vinylphenol compound include ones in which R⁶ R⁷,R⁸, and R⁹ are each a hydrogen atom or an alkyl group, provided that atleast one of R⁷ and R⁹ is a hydrogen atom. As such vinylphenolcompounds, mention may be made of, for example, 4-vinylphenol,4-vinyl-2-methylphenol, 4-vinyl-3-methylphenol, 4-vinyl-2-ethylphenol,4-vinyl-3-ethylphenol, 4-vinyl-2-n-propylphenol,4-vinyl-3-n-propylphenol, 4-vinyl-2-isopropylphenol,4-vinyl-3-isopropylphenol, 4-vinyl-2-n-butylphenol,4-vinyl-3-n-butylphenol, 4-vinyl-2-s-butylphenol,4-vinyl-3-s-butylphenol, 4-vinyl-2-t-butylphenol,4-vinyl-3-t-butylphenol, 4-vinyl-2,3-diemthylphenol,4-vinyl-2,5-diemthylphenol, 4-vinyl-3,5-dimethylphenol,4-vinyl-2,3,5-trimethylphenol, etc.

Particularly preferred vinylphenol compounds are those in which two orthree out of R⁶ to R⁹ are alkyl groups and the remaining ones arehydrogen atoms. As such vinylphenol compounds, mention may be made of,for example, 4-vinyl-2-methylphenol, 4-vinyl-2,6-dimethylphenol,4-vinyl-2,3,6-trimethylphenol, etc.

Other preferred vinylphenol compounds include ones in which R⁶, R⁷, R⁸,and R⁹ are each a hydrogen atom, an alkoxy group, a hydroxyl group or ahalogen atom. As such vinylphenol compounds, mention may be made of, forexample, 4-vinyl-2-methoxyphenol, 4-vinyl-3-methoxyphenol,4-vinyl-2-hydroxyphenol, 4-vinyl-3-hydroxyphenol,4-vinyl-2,6-difluorophenol, etc.

The above isopropenylphenol compound is a compound that has anisopropenyl group (CH₂═CCH₃—) at the para-position with respect to thephenolic hydroxyl group and includes those compounds represented by theabove general formula (II) in which R⁶ to R⁹ independently represent ahydrogen atom, an alkyl group, an alkoxy group, an aryl group, anaralkyl group, a hydroxyl group or a halogen atom, provided that atleast one of R⁷ and R⁹ is a hydrogen atom.

The alkyl groups in the substituents R⁶ to R⁹ are preferably linear,branched or cyclic and have one or more and 10 or less carbon atoms. Assuch alkyl groups, mention may be made of, for example, a methyl group,an ethyl group, an isopropyl group, a t-butyl group, a 2-ethylhexylgroup, a cyclohexyl group, etc.

The alkoxy groups in the substituents R⁶ to R⁹ preferably have 1 or moreand 4 or less carbon groups. As such alkoxy groups, mention may be madeof, for example, a methoxy group, a propoxy group, a t-butoxy group,etc.

The aryl groups in the substituents R⁶ to R⁹ include preferably a phenylgroup, a naphthyl group, a tolyl group, a cumyl group, etc.

The aralkyl groups in the substituents R⁶ to R⁹ preferably have 6 ormore and 10 or less carbon atoms. As such aralkyl groups, mention may bemade of, for example, a benzyl group, a phenethyl group, a1-methyl-1-phenylethyl group, etc.

Those preferred as the isopropenylphenol compound include ones in whichR⁶ R⁷, R⁸, and R⁹ are independently a hydrogen atom or an alkyl group,provided that at least one of R⁷ and R⁹ is a hydrogen atom. As suchisopropenylphenol compounds, mention may be made of, for example,4-isopropenylphenol, 4-isopropenyl-2-methylphenol,4-isopropenyl-3-methylphenol, 4-isopropenyl-2-ethylphenol,4-isopropenyl-3-ethylphenol, 4-isopropenyl-2-n-propylphenol,4-isopropenyl-3-n-propylphenol, 4-isopropenyl-2-isopropylphenol,4-isopropenyl-3-isopropylphenol, 4-isopropenyl-2-n-butylphenol,4-isopropenyl-3-n-butylphenol, 4-isopropenyl-2-s-butylphenol,4-isopropenyl-3-s-butylphenol, 4-isopropenyl-2-t-butylphenol,4-isopropenyl-3-t-butylphenol, 4-isopropenyl-2,3-diemthylphenol,4-isopropenyl-2,5-diemthylphenol, 4-isopropenyl-3,5-dimethylphenol,4-isopropenyl-2,3,5-trimethylphenol, etc.

Other preferred isopropenyl compounds include ones in which R⁶, R⁷, R⁸,and R⁹ are each a hydrogen atom, an alkoxy group, a hydroxyl group or ahalogen atom. As such isopropenylphenol compounds, mention may be madeof, for example, 4-isopropenyl-2-methoxyphenol,4-isopropenyl-3-methoxyphenol, 4-isopropenyl-2-hydroxyphenol,4-isopropenyl-3-hydroxyphenol, 4-isopropenyl-2,6-difluorophenol, etc.

The compound (A) is reacted (condensed) with the polymerizable phenolcompound, which is a vinylphenol compound or isopropenyl compound, orthe polymer (B), which is a polymer of the polymerizable compound. Thepolymer (B) is preferably one that is obtained by preliminarilypolymerizing at least one compound selected from the vinylphenolcompounds and isopropenylphenol compounds described above by livinganion polymerization or radical polymerization at the site of the doublebond and has a weight average molecular weight of about 500 to 20,000,particularly 2,000 to 20,000.

As the polymer (B), mention may be made of, for example, a homopolymer(C) obtained by use of a compound selected from the above vinylphenolcompounds and isopropenyl compounds, a copolymer (D) obtained by use ofat least two compounds of the above vinylphenol compounds andisopropenyl compounds, and a copolymer (E) obtained by use of at leastone compound selected from the above vinylphenol compounds andisopropenyl compounds and at least one other monomer.

As the homopolymer (C), mention may be made of, for example,polyparahydroxystyrene, polyparahydroxy-α-methylstyrene, etc.

As the copolymer (E), those obtained by copolymerizing the polymerizablephenol compound represented by the general formula (II) above(hereafter, sometimes referred to simply as polymerizable phenolcompound) and other copolymerizable monomer by radical polymerization orthe like using about 50 mol % or more, preferably 60 mol % or more ofthe polymerizable phenol based on the total moles of the polymerizablephenol and the copolymerizable monomer.

Novolak type phenol resin obtained by reacting the copolymer (E) and thecompound (A) gives rise to resist patterns excellent in heat resistance,sensitivity, and resolution.

As the other copolymerizable monomer, mention may be made of, forexample, styrenes, acrylic acid and ester derivatives thereof,α-substituted acrylic acid and ester derivatives thereof. As thestyrenes, mention may be made of, for example, styrene, substitutedstyrenes, etc. As the acrylic acid and ester derivatives thereof,mention may be made of, for example, acrylic acid, methyl acrylate, etc.As the α-substituted acrylic acid and ester derivatives thereof, mentionmay be made of, for example, methacrylic acid, ethyl methacrylate,tertiary butyl methacrylate, etc.

As the copolymer (E), the copolymers of the above polymerizable phenolcompound, styrenes and (meth)acrylic acid esters are preferred. As suchcopolymer (E), mention may be made of, for example, copolymers obtainedby copolymerization of the above polymerizable phenol compound withtertiary butyl methacrylate, etc.

The phenol resin of the present invention can be produced advantageouslyby condensing at least two components, i.e., the above polymerizablephenol compound or polymer (B) and the compound (A), in a ratio of 1 to50 moles, preferably 5 to 20 moles of the compound (A) per 100 moles ofthe above polymerizable phenol compound or 100 moles of polymerizablephenol compound as the structural unit contained in the polymer (B) inthe presence of an acid. If the ratio of the compound (A) is less than 1mole, the improvement that can be expected in the pattern shape ofresists may not be large. If the ratio of the compound (A) exceeds 50moles, the decrease in sensitivity is too great to be practical.

The above acid is used as an acid catalyst. As the acid catalyst,mention may be made of, for example, inorganic acids such ashydrochloric acid. Soluble, fusible resins obtained by condensation ofphenols with acid catalysts are called novolak type resins.

The phenol resin of the present invention has a weight average molecularweight (hereafter, referred to as Mw) in the range of 2,000 to 20,000.If the Mw of the phenol resin is below 2,000, it is difficult to obtainresist patterns excellent in heat resistance, etc. If the Mw of thephenol resin is above 20,000, there arises the problem that it isdifficult to dissolve in solvents such as ethyl lactate. Condensationtime, etc., can adjust the Mw of the phenol resin.

As the method for producing the phenol resin, mention may be made of,for example, a method that comprises charging the compound (A) and thepolymerizable phenol compound or the polymer (B) in a reactor in a ratiosuch that the amount of the compound (A) is 1 to 50 moles per 100 molesof the polymerizable phenol compound or 100 moles of the polymerizablephenol compound as the structural unit contained in the polymer (B) andcondensing the compound (A) with the polymerizable phenol compound orthe polymer (B) in a state dissolved in a solvent such as analcohol-based solvent in the presence of an acid catalyst at atemperature of about 50 to 100° C. Precipitation of the produced phenolresin in water or the like followed by purification and drying theprecipitate results in a phenol resin in the form of a powder.

Substituted phenol resins of which about 10 to 50 mol % of the hydroxylgroups of the phenol resin has been substituted by alkoxygroups arepreferable as a resin for forming resist patterns. Substituted phenolresins have the property of becoming alkali soluble as a result ofelimination of alkoxy groups due to acid generated by an photo-acidgenerator and then elimination of all the alkoxy groups by chemicalamplification.

The substituted phenol resin can be obtained in the form of a powder bydissolving an unsubstituted phenol resin in a solvent (for example, anester-based solvent such as ethyl acetate), adding to the resultingsolution an alkoxylating agent (for example, di-tertiary butyldicarbonate) and an alkoxylating catalyst (for example, a tertiary aminecompound such as triethylamine) to substitute a portion of the phenolichydroxyl groups into alkoxy groups, precipitating the resulting resin,and purifying and drying the precipitate.

The phenol resin of the present invention is useful as a resin forresists for use in the formation of resist patterns. A resist patterncan be formed, for example, by preparing a resist solution containingthe phenol resin of the present invention, an photo-acid generator, anda solvent (for example, ethyl lactate), coating the resist solution on asubstrate to form a resist film, exposing the resist film to light anddeveloping it. Such a resist pattern is useful for the production ofintegrated circuits, etc. Here, as the photo-acid generator, mention maybe made of diazo compounds such as bis(cyclohexylsulfonyl)diazomethane.

EXAMPLES

Hereafter, the present invention will be described concretely byexamples. In the following examples and comparative examples, all partsare by weight.

Example 1

Production of a Novolak Type Phenol Resin

In a separable flask, 150 g of polyparahydroxystyrene (Mw: 5,000)synthesized by a known method (0.0375 mole as polyparahydroxystyrene[containing 150/120 moles=1.25 moles as parahydroxystyrene unit(molecular weight: 120)]) and 300 g of methanol were charged andpolyparahydroxystyrene was dissolved in methanol. After dissolving, 130g of 35% HCl was added and the resulting mixture was stirred at roomtemperature. During the stirring, a methanol solution containing 20 g(0.132 mole) of 4-hydroxymethyl-2,6-dimethylphenol dissolved in methanolin advance was added dropwise over 1 hour at room temperature. After theaddition, the temperature was elevated and a reaction was carried outfor 8 hours under ref lux of methanol. After completion of the reaction,the reaction mixture was cooled down to room temperature and thereaction mixture was added dropwise into 3,000 g of deionized water toprecipitate a resin, which was collected by filtration. The collectedresin was washed with 1,000 g of deionized water and collected byfiltration. This purification step was repeated 5 times. Then, theobtained resin was dried at 40° C. to obtain 160 g of novolak typephenol resin (Mw: 6,000). The Mw was measured by gel permeationchromatography (GPC).

In this example, the charged amount of4-hydroxymethyl-2,6-dimethylphenol was in a ratio of 13.3 parts per 100parts of polyparahydroxystyrene charged. The mole number (molar ratio)of 4-hydroxymethyl-2,6-dimethylphenol was in a ratio of 10.6 moles(=0.132×100/1.25 moles) per 100 moles of the structural unit ofparahydroxystyrene in polyparahydroxystyrene.

The mole ratio of the charged compound (A) and the mole ratio of thecharged polymerizable phenol compound are identical with the mole ratioof the structural unit of compound (A) in the phenol resin to bepolymerized and the ratio of the mole number of the structural unit ofpolymerizable phenol compound, respectively. Therefore, the novolak typephenol resin obtained by condensation in this example contained thestructural unit of 4-hydroxymethyl-2,6-dimethylphenol (compound A) in aratio of 10.6 moles per 100 moles of the structural unit ofparahydroxystyrene.

Production of Substituted Phenol Resin

The obtained novolak type phenol resin (100 g) was dissolved in 200 g ofethyl acetate, to which 55 g of di-tertiary butyl dicarbonate and 28 gof triethylamine were added and the mixture was reacted for 5 hoursunder reflux. After the reaction, 300 g of ethylene glycol monoethylether was added as a solvent and ethyl acetate was removed under reducedpressure. Then, the reaction mixture was added dropwise into 3,000 g ofdeionized water to precipitate a resin, which was collected byfiltration. The collected resin was washed with 1,000 g of deionizedwater and collected by filtration. This purification step was repeated 5times. Then, the obtained resin was dried at 40° C. to obtain 120 g of asubstituted phenol resin, i.e., the above novolak type phenol resin ofwhich 36 mole % of the phenolic hydroxyl groups was substituted bytertiary butoxy groups.

Formation of Resists Patterns

The obtained substituted phenol resin (100 g) and 5 g of photo-acidgenerator (bis(cyclohexylsulfonyl)diazomethane) were dissolved in 400 gof ethyl lactate to prepare a resist solution. The resist solution wasfiltered through a 0.2 μm membrane filter to obtain a resist solution.The resist solution was coated on a silicon wafer (substrate) using aspinner and the coated wafer was dried on a hot plate at 90° C. for 90seconds to produce a resist film of 0.7 μm in thickness. This film wasimagewise exposed to light using a reduced projection aligner and thenheated at 110° C. for 90 seconds. Then, it was developed with an aqueous2.38 wt % tetramethylammonium hydroxide solution for 30 seconds andrinsed with deionized water. The silicon wafer with a resist patternafter the development was left to stand in a clean oven set to varioustemperatures for 30 seconds and then the resist pattern was observedusing a scanning electron microscope to evaluate the shape of thepattern and the like. The results of the observation are shown in Table1.

Example 2

A novolak type phenol resin (Mw: 8,000) was obtained by repeating thesame procedures as in Example 1 except that 150 g ofpolyparahydroxystyrene (Mw: 7,000) synthesized by a known method wasused instead of 150 g of the polyparahydroxystyrene (Mw: 5,000) inExample 1. Then, a substituted phenol resin was obtained in the samemanner as in Example 1 except that 100 g of this novolak type phenolresin was used instead of 100 g of the novolak type phenol resin inExample 1. A resist pattern was formed in the same manner as in Example1 except that 100 g of the substituted phenol resin was used instead of100 g of the substituted phenol resin in Example 1 and the shape ofpattern and the like of the formed resist pattern were evaluated byobservation using a scanning electron microscope. The results are shownin Table 1.

Example 3

A novolak type phenol resin (Mw: 8,100) was obtained by repeating thesame procedures as in Example 1 except that 21.8 g (0.131 mole) of4-hydroxymethyl-2,3,6-trimethylphenol was used instead of 20 g of4-hydroxymethyl-2,6-dimethylphenol in Example 1. In this example, themole number of charged 4-hydroxylmethyl-2,3,6-trimethylphenol (compound(A)) was in a ratio of 10.5 moles per 100 moles of the structural unitof parahydroxystyrene. Then, a substituted phenol resin was obtained inthe same manner as in Example 1 except that 100 g of this novolak typephenol resin was used instead of 100 g of the novolak type phenol resin.A resist pattern was formed in the same manner as in Example 1 exceptthat 100 g of the substituted phenol resin was used instead of 100 g ofthe substituted phenol resin in Example 1 and the properties of theformed resist pattern were evaluated in the same manner as in Example 1.The results are shown in Table 1.

Example 4

A novolak type phenol resin (Mw: 8,000) was obtained by repeating thesame procedures as in Example 1 except that 150 g (0.0214 mole ascopolymer, or 1.26 moles as parahydroxystyrene unit) ofparahydroxystyrene/styrene/tertiary butyl methacrylate copolymer (molarratio of structural units of the copolymer components: 7/2/1, Mw: 7,000)synthesized by a known method was used instead of 150 g of thepolyparahydroxystyrene (Mw: 5,000) of Example 1. In this example, themole number of charged 4-hydroxylmethyl-2,6-dimethylphenol (compound(A)) was in a ratio of 1.04 moles per 100 moles of the structural unitof parahydroxystyrene in the parahydroxystyrene/styrene/tertiary butylmethacrylate copolymer [that is, structural units of polymerizablephenol compound contained in the polymer (B)] . Then, a substitutedphenol resin was obtained in the same manner as in Example 1 except that100 g of this novolak type phenol resin was used instead of 100 g of thenovolak type phenol resin in Example 1 and that 40 g of di-tertiarybutyl dicarbonate was used instead of 55 g of di-tertiary butyldicarbonate in Example 1. A resist pattern was formed in the same manneras in Example 1 except that 100 g of the substituted phenol resin wasused instead of 100 g of the substituted phenol resin in Example 1 andthe properties of the formed resist pattern were evaluated in the samemanner as in Example 1. The results are shown in Table 1.

Comparative Example 1

For comparison with Examples 1, 2 and 3, a polyparahydroxystyrene resin(Mw: 6,000) was synthesized by a known method. A substituted phenolresin was obtained in the same manner as in Example 1 except that 100 gof this polyparahydroxystyrene resin was used instead of 100 g of thenovolak type phenol resin of Example 1. A resist pattern was formed inthe same manner as in Example 1 except that 100 g of the substitutedphenol resin was used instead of 100 g of the substituted phenol resinof Example 1. The resist pattern was observed using a scanning electronmicroscope to evaluate the pattern shape and the like of the formedresist. The results are shown in Table 1.

Comparative Example 2

For comparison with Example 4, a parahydroxystyrene/styrene/tertiarybutyl methacrylate copolymer (molar ratio of structural units of thecopolymer components: 7/2/1, Mw: 8,000) was synthesized by a knownmethod. A substituted phenol resin was obtained in the same manner as inExample 4 except that 100 g of the parahydroxystyrene/styrene/tertiarybutyl methacrylate copolymer was used instead of 100 g of the novolaktype phenol resin of Example 4. A resist pattern was formed in the samemanner as in Example 1 except that 100 g of the substituted phenol resinwas used instead of 100 g of the substituted phenol resin of Example 4and the properties thereof were evaluated in the same manner as inExample 4. The results are shown in Table 1.

The methods for determining the pattern shape and the like shown inTable 1 were as follows.

Pattern shape: The shape of the resist pattern after heating at 110° C.is shown in a magnified state in Table 1.

Heat resistance: When a resist pattern was heated, the temperature atwhich the resist pattern showed thermal deformation is shown in Table 1.

Sensitivity: Light exposure at which a 0.25 μm line and space wereresolved at 1:1 is shown in Table 1 as the optimal exposure (Em).

Resolution: At the light exposure at which a 0.25 μm line and space wereresolved at the 1:1, the minimum line width of a separated line andspace was defined as the resolution of the evaluated resist.

TABLE 1 Heat Pattern resistance Sensitivity Resolution shape (° C.)(mJ/cm²) (μm) Example 1

135 34 0.20 Example 2

135 36 0.20 Example 3

135 40 0.20 Example 4

130 42 0.20 Comparative Example 1

135 50 0.22 Comparative Example 2

130 55 0.22

The mole number of charged compound (A), the mole number of thestructural unit of polymerizable phenol compound in the polymer (B), theratio of the mole number of charged compound (A) per 100 moles of thestructural unit of the polymerizable phenol compound, and the Mw of theobtained novolak type phenol resin upon production of a novolak typephenol resin for Examples 1 to 4 are shown in Table 2.

TABLE 2 Mole number of Mole number structural unit of Molar ratio of ofcompound (A) polymerizable phenol compound (A) Mw of phenol resinExample 1 0.132 1.25 10.6 6,000 Example 2 0.132 1.25 10.6 8,000 Example3 0.131 1.25 10.5 8,100 Example 4 0.131 1.26 10.4 8,000

Table 1 indicates that the resist patterns of Examples 1 to 4 aresuperior to the resist patterns in Comparative Examples 1 and 2 in heatresistance, without showing rounded corners of the top portion of theresist pattern, and also in sensitivity and resolution. The resistpatterns of Examples 1, etc. are summarized as follows.

Resist patterns of Examples 1 to 3: Resist pattern using the substitutedphenol resin obtained by co-condensing the compound (A) and thehomopolymer of polymerizable phenol compound and alkoxylating theco-condensation product.

Resist pattern of Example 4: Resist pattern using the substituted phenolresin obtained by co-condensing the compound (A) and theparahydroxystyrene/styrene/tertiary butyl methacrylate copolymer(copolymer of polymerizable phenol compound) and alkoxylating theco-condensation product.

Resist pattern of Comparative Example 1: Resist pattern using thesubstituted phenol resin obtained by alkoxylating the homopolymer ofpolymerizable phenol compound.

Resist Pattern of Comparative Example 2: Resist pattern using thesubstituted phenol resin obtained by alkoxylating theparahydroxystyrene/styrene/tertiary butyl methacrylate copolymer.

What is claimed is:
 1. A phenol resin obtained by reacting at least twocomponents, i.e., a compound (A) represented by the following generalformula (I) and a polymerizable phenol compound represented by thefollowing general formula (II) or a polymer (B), which is a polymer ofthe polymerizable phenol compound, in a ratio of 1 to 50 moles of thecompound (A) to 100 moles of the polymerizable phenol compound or 100moles of a structural unit of the polymerizable phenol compoundcontained in the polymer (B) in the presence of an acid and having aweight average molecular weight of 2,000 to 20,000

(wherein R¹, R², R³, and R⁴, which are the same or different,independently represent a hydrogen atom, an alkyl group, an alkoxygroup, an aryl group, an aralkyl group, a hydroxyl group or a halogenatom)

(wherein R⁵ represents a hydrogen atom or a methyl group, R⁶, R⁷, R⁸,and R⁹, which are the same or different, independently represent ahydrogen atom, an alkyl group, an alkoxy group, an aryl group, anaralkyl group, a hydroxyl group or a halogen atom, provided that atleast one of R⁷ and R⁹ is a hydrogen atom).
 2. The phenol resin asclaimed in claim 1, wherein the polymer (B) is a homopolymer of thepolymerizable phenol compound, or a copolymer of at least one monomerselected from the group consisting of styrenes, acrylic acid,α-substituted acrylic acid and ester derivatives thereof with thepolymerizable phenol compound.
 3. A phenol resin comprising the phenolresin of claim 1, wherein at least a portion of the hydroxyl groups ofthe phenol resin is substituted by alkoxy groups.
 4. The phenol resin asclaimed in claim 1, wherein the phenol resin is a resin for resists.